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5.5.1 Portability of C Functions

Most usual functions can either be missing, or be buggy, or be limited on some architectures. This section tries to make an inventory of these portability issues. By definition, this list will always require additions. Please help us keeping it as complete as possible.

The ISO C99 standard says that if the output array isn't big enough and if no other errors occur, snprintf and vsnprintf truncate the output and return the number of bytes that ought to have been produced. Some older systems return the truncated length (e.g., GNU C Library 2.0.x or IRIX 6.5), some a negative value (e.g., earlier GNU C Library versions), and some the buffer length without truncation (e.g., 32-bit Solaris 7). Also, some buggy older systems ignore the length and overrun the buffer (e.g., 64-bit Solaris 7).

The ISO C standard says sprintf and vsprintf return the number of bytes written, but on some old systems (SunOS 4 for instance) they return the buffer pointer instead.

The POSIX spec says that unlink causes the given files to be removed only after there are no more open file handles for it. Not all OS's support this behaviour though. So even on systems that provide unlink, you cannot portably assume it is OK to call it on files that are open. For example, on Windows 9x and ME, such a call would fail; on DOS it could even lead to file system corruption, as the file might end up being written to after the OS has removed it.

Signed >>
Normally the C >> right shift of a signed type replicates the high bit, giving a so-called "arithmetic" shift. But care should be taken since the ISO C standard doesn't require that behaviour. On those few processors without a native arithmetic shift (for instance Cray vector systems) zero bits may be shifted in, the same as a shift of an unsigned type.

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This document was generated by Charlie & on October, 19 2001 using texi2html